Plug-in high-power waveguide junction circulator

ABSTRACT

The disclosure describes an isolator for detachable installation in a rectangular waveguide transmission line, realized in a three-port waveguide junction circulator having a matchedimpedance termination at one port. The circulator is in a rigid section of rectangular waveguide dimensioned to fit closely within the transmission line, in which it can be installed through an aperture in a side wall. When the isolator is installed in the transmission line, the isolator ports couple into the junction microwave energy flowing therein, and the third-port termination is external to the transmission line, where it can be cooled. The waveguide structure for the circulator and third-port termination can be made of two identical rigid castings which mate to form enclosures for the circulator and termination components. Uses of the isolator in a microwave heating oven are described.

United States Patent [1 1 Carr et al.

PLUG-IN HIGH-POWER WAVEGUIDE JUNCTION CIRCULATOR Inventors: Kenneth L. Carr, Bedford; Sumner Segal, Newton Centre, both of Mass.

Microwave Associates, Inc., Burlington, Mass.

Filed: Dec. 14, 1972 Appl. No.: 315,176

Assignee:

References Cited UNITED STATES PATENTS 7/1970 Hagler et al. 333/242 x 12/1968 Caswell 333/242 7/1965 ,Chang 333/l.l X

[451 Apr. 23, 1974 Primary Examiner-Paul L. Gensler Attorney, Agent, or Firm-Alfred H. Rosen; Frank A. Steinhilper [5 7] ABSTRACT The disclosure describes an isolator for detachable installation in a rectangular waveguide transmission line, realized in a three-port waveguide junction circulator having a matched-impedance termination at one port. The circulator is in a rigid section of rectangular waveguide dimensioned to fit closely within the transmission line, in which it can be installed through an aperture in a side wall. When the isolator is installed in the transmission line, the isolator ports couple into the junction microwave energy flowing therein, and the third-port termination is external to the transmission line, where it can be cooled. The waveguide structure for the circulator and third-port termination can be made of two identical rigid castings which mate to form enclosures for the circulator and termination components. Uses of the isolator in a microwaveheating oven are described.

22 Claims, 13 Drawing Figures SOURCE PLUG-IN HIGH-POWER WAVEGUIDE JUNCTION CIRCULATOR BACKGROUND OF THE INVENTION In the art of microwave cooking, microwave energy in a selected frequency range is supplied via appropriate waveguide structures to an enclosure which may be regarded as the equivalent of an oven. In fact the oven is not heated. Only the foodstuff that is placed in it is heated, by extracting energy from the microwave energy that is present in the oven. The oven itself, and a plate on which the foodstuff may rest, usually remain cool or even cold. Several problems that are unique to the handling of microwave energy are presented to makers and users of microwave ovens. Chief among these are problems of standing wave patterns, problems of leakage of microwave energy around the door giving a user access to the oven, and the problems of changing microwave load presented by an oven as the foodstuff in it is cooked and loses its moisture. The effects of these problems are not segregated, but rather they interact, to further complicate the des'igners tasks.

A standing-wave'pattern of microwave energy will not cook food uniformly, so it is customary to provide some means to stir the wave energy into a random distribution. One usual device provided for this purpose is a metal fan rotating in the oven to cause random reflections of the microwave energy. Stirring the microwave energy presents a load to the microwave source that varies in impedance in a random fashion. Such a load cannot be optimally matched to its source, and some energy, the amount of which changes in a random way, will be reflected back toward the source.

For efficiency, and because microwave energy can be injurious to the health of persons, the oven door is fitted with means to prevent leakage of microwave energy around the door when it is closed and the oven is operating. Microwave choke configurations, cooperating in the'peripheries of the door and the surrounding frame, are customarily used, but these are frequency-sensitive and therefore must be tuned to the operating frequency. However, microwave sources, customarily magnetrons, emit some second harmonic-frequency energy, and a choke that is turned to a given fundamental frequency will not stop the second harmonic of that frequency. Accordingly, it is usual to add a gasket made of a pliable material such as rubber that is impregnated or otherwise loaded with a microwave absorber such as carbon, to absorb the energy that is not stopped by the choke. Such gaskets cost money and they waste energy and generate unwanted heat.

Foodstuffs are cooked by microwave energy through a process in which the energy is absorbed by water contained in the foodstuffs, and turns to vapor. Raising the temperature of the water raises the temperature of the foodstuff. The water is the energy absorber. When the water is all gone off as vapor, cooking stops. Thus, a load which starts off essentially as a water load to the microwave energy tends eventually to become no load at all, and an increasing amount of the microwave energy is fed back toward the source.

The nature of these problems has been recognized for some time, and some solutions have been proposed to minimize them. D. A. Copson, Microwave Heating in FreezeDrying, Electronic Ovens, and Other Applications, The AV! Publishing Company, Inc., Westport, Conn., 1962, at page 156, in a passage entitled ISOLATORS" states Where it is necessary to reduce reflections back to the power tubes to a minimum, microwave energy isolators of the ferrite or similar type may be used. These isolators consist of a slim strip of ferrite upon which a permanent magnetic field is imposed. Under these conditions the waveguide acts to transmit one way only; the isolator absorbing reflection. For full effect the isolator is cooled so that absorbed energy cannot change its characteristics. Insertion of the device results in a slight loss in efficiency but extension of tube life makes the added cost attractive. High frequency applications of ferrites have been covered in the book by Roberts (1960). J. Roberts, High Frequency Applications of Ferrites, D. Van Nostrand Company, Inc., 1960, at page 81 illustrates in FIG. 3.9(b) and describes how an isolator may be realized through the agency of a circulator having three or more ports. A three-port circulator is shown, having three terminals labelled, respectively, 1, 2 and 3. A matched load is connected to terminal 2. Power entering at terminal l of the circulator is fed to terminal 2 and absorbed in the matched load. Power entering at terminal 3 passes freely to terminal 1. Thus, terminals 1 and 3 serve as the isolator ports.

Copson's teaching is found in U.S. Pat. No. 3,210,513 to Lenart, the stated object of which is to prevent microwave energy reflected in the cavity from being transmitted back to the magnetron, and this is done by providing a waveguide between the magnetron and the cavity through which microwave energy can pass only in one direction from the magnetron to the cavity. FIG. 3 of that patent shows a branch waveguide containing dielectric loss material for absorbing the reflected microwave energy. Copsons comment that the isolator is cooled so that absorbed energy cannot change-its characteristic finds early recognition in U.S. Pat. No. 3,010,086, teaching that isolators employing materials having gyromagnetic properties are temperature and frequency sensitive, and showing that if heat generated in the gyromagnetic material is dissipated to the surrounding environment its power handling capabilities will be increased. Further recognition is found in U.S. Pat. No. 2,922,878, FIG. 3B of which shows a waveguide containing two thin slabs of ferrite material positioned against two opposite walls of the waveguide, giving the advantage that heat is readily conducted from the ferrite element through the wall of the waveguide to which it is secured, the efficient conduction of heat from the ferrite being stated to be an important consideration in maintaining a wide useful range of operability for the device employing these ferrite components. Again in U.S. Pat. No. 3,075,159 to Skomal it is taught to mount ferrite specimens on one or more walls of a waveguide isolator to promote dissipation of heat by conduction through the wall. Bowness in U.S. Pat. No. 3,136,962 shows two ferrite buttons mounted on the opposite inner walls of a multi-port waveguide circulator developed from a Y-Circulator, with a dielectric matching member between them. The need to remove heat for applications of ferrite devices such as Y- circulators when the power is greater than about 1 kilowatt is treated again in U.S. Pat. No. 3,246,262 where, in order to remove heat from a ferrite body that is not in contact with a waveguide wall, a thermallyconductive dielectric is arranged between the ferrite and the wall, for example, in a Y-circulator. U.S. Pat. No. 3,231,835 shows in FIGS. 4 and 5 a three-port circulator in an I-I-plane T-Junction having two slabs of ferrite material mounted one against each of the opposite inner waveguide walls in the junction.

The teaching of Roberts is expressed in US. Pat. No. 3,070,760 to Wheeler, who shows at FIG. 8 a threeport circulator in an H-plane T-junction in rectangular waveguide, transformed into an isolator by the simple expedient of adding a matched load and a shorting plate to one waveguide arm.

Teachings of the above-described prior art appear in US. Pat. Nos. to 3,437,777 and to 3,670,134, each of which employs an isolator of an I-I-plane T-junction rectangular waveguide circulator as shown in Wheeler, interposed in a waveguide joining a magnetron and a microwave heating apparatus or oven. Typically, the isolator is an integral part of the entire waveguide structure, and this leads to complexities in building and servicing the apparatus. There is no way to get access to the circulator to make repairs to it, if necessary, short of disassembling or destroying the waveguidefeed structure. Moreover, since the waveguide structure is generally made of sheet metal in the interest of low cost, the rigidity that is important to reliable functioning of a microwave circulator cannot be assured, and it appears that up to now little or no practical use has been made in microwave ovens of the well-known desirable properties of isolators that can be realized in rectangular waveguide junctions; The present invention has as its objects to correct these deficiencies.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an H-plane isolator according to the invention outside a main rectangular waveguide in position for installation therein through an aperture in a narrow wall of the main waveguide;

FIG. 1A schematically shows the isolator inserted in the main waveguide as proposed in FIG. I;

F IG. 2 is a longitudinal section of the isolator taken along line 2--2 of FIG. 1;

FIG. 3 is an exploded view of the isolator in FIGS. 1 and 2;

FIG. 4 shows a modification of the isolator of FIG. 1;

FIG. 5 shows another embodiment of the invention, employing an E-plane isolator, in position for installation in a main rectangular waveguide through an aperture in a wide wall thereof;

FIG. 6 is a side view of the isolator of FIG. 5 from the plane of line 6-6;

FIG. 7 is an isometric view of a microwave heating apparatus incorporating a modified form of the present invention;

FIG. 8 is a section along line 88 of FIG. 7;

FIG. 9 is an electrical schematical diagram illustrating the operation of FIG. 7;

FIG. 10 is a partial cross section of a component of FIG. 7;

FIG. 11 illustrates a microwave heating apparatus incorporating an E-plane isolator; and

FIG. 12 shows a modification of FIG. 5 suitable for. use in the apparatus of FIG. 11.

DETAILED DESCRIPTION OF THE DRAWINGS In FIG. 1, a main rectangular waveguide 10, shown as a section of the waveguide between two arms 1 1, 12, which may for example be connected between a source (such as a magnetron) at one arm 11 and a load (such as a microwave heating oven) at the other arm 12, has a rectangular aperture 17 in one of its narrow walls 13. Neither a source nor a load is shown, it being understood that these may be found in the prior art as exemplified by either of the US Pats. No.s 3,437,777 or 3,670,134 mentioned above. The waveguide 10 is com posed of wide walls 15, 16 and narrow walls 13, 14 having, respectively, a known internal width dimension and a known internal height dimension. The aperture 17 extends in a width W (between the wide walls) coextensively with the internal height dimension, so that its width is the full internal height of the main waveguide 10. The length L of the aperture 17 axially of the waveguide 10 is prescribed by the size of the opening needed to accommodate the isolator of the invention. For reasons that will presently appear, the main waveguide 10 may be made of sheet metal, and is not required to supply rigidity in the circulator region.

An isolator '20 according to the invention is assembled from two identical parts 21 and 22, the construction of which is illustrated in greater detail in FIGS. 2 and 3. When the two parts are assembled, the isolator is in two principal sections, the first of which 23 is a circulator section intended to fit within the main waveguide 10 and includes the components of a rectangular waveguide three-port circulator (not shown in FIG. 1),

v and the second of which 24 constitutes a branch waveguide terminated in a matched load (not shown in FIG. 1) and closed at its outermost end 25. The circulator section also optionally includes an iris opening 26 in one or both ends 27, 28, respectively, that open into the main waveguide, for second-harmonic filtering purposes, as will presently be explained. A magnetic yoke 29, in the form of a generally U-shaped soft iron strap, is fitted over the circulator section 23, to serve as part of the magnetic circuit usually associated with a ferrite circulator. f

The isolator 20 is installed in the main waveguide 10 by fitting the first section 23 through the rectangular aperture 17 and across the waveguide so that the external flanges 31, 32 are flush with the exterior of the narrow wall 13 at both ends of the aperture. These flanges can also function as locating stops for the circulator section 23. The isolator is fastened to the waveguide with screw-bolts 33 passing through holes 34 in the flanges and threadedly engaging holes 35 in the narrow wall 13 of the waveguide. The completed installation, as is schematically illustrated in FIG. 1A, provides a three-port H-plane T-junction waveguide circulator having two ports within the arms 11 and 12. Flanges 37, 38, extending parallel to the planes of the circulator waveguide ends 27, 28, respectively, preferably make electrical contact with the inner walls of the main waveguide 10.

The two parts 21 and 22 of the isolator 20 are preferably made by die-casting techniques that are commonly used in making microwave waveguide systems components. As is mentioned above, they are identical, and the structural features of each are illustrated in FIGS. 2 and 3. Two ferrite discs 41, 42 are located in the circulator junction region 23 with a dielectric separator 43 between them. The inner wall 45, 46 of the each part 21, 22, respectively, is counter-bored at 51, 52, respectively, to provide recesses for receiving and locating the ferrite discs 41, 42, respectively, at one side of each, and the separator 43 has corresponding counterbores in its outer faces to receive and locate the confronting faces of the ferrite discs. The dielectric separator 43 is made of a suitably resilient material, such as Teflon (a plastic consisting of a tetrafluoroethylene polymer), and the thicknesses of the ferrite members 41, 42 and the separator 43 are so chosen that, when the two parts 21, 22 are assembled the stack composed of the ferrite members with the separator between them will compress the separator slightly. This precaution assures that, in the event of failure of a cement used to hold one or the other of the ferrite discs in place in a recess 51 or 52 the expansive force exerted by the separator 43 will nevertheless hold that disc in place, and thereby prevent electrical failure of the circulator. This feature, which is realizable in a circulator made of rigid waveguide, is difficult if not impossible to achieve when sheet metal waveguide is used. It constitutes an advantage when used in microwave ovens intended for domestic consumer usage, where the user is not technically sophisticated and might unknowingly be exposed to microwave radiation in the event of failure of the isolator. The separator 43, shown herein as made in one piece, may be made of two identical pieces separated in a plane parallel to the confronting faces of the ferrite discs.

The outer wall of each part 21, 22 respectively, is counter-bored at 61, 62, respectively, to provide recesses for receiving and locating permanent magnet pole pieces 63, 64, respectively, adjacent the ferrite discs- 41, 42, respectively, to provide the required magnetic field for circulator action. The magnetic yoke 29 serves not only as the customary magnetic circuit element, but also as a spring to hold the pole pieces in their respective recesses.

The second section 24 of the isolator is fitted with microwave absorber load pieces 71, 72 (FIG. 2), respectively, which may be cemented in place, and which with the storing plate 25 constitutes a matched load for the third arm of the circulator, whereby to transform a three-port circulator into an isolator as is taught by Wheeler, above cited. Heat generated in the load pieces may be dissipated in part by fins 73 formed in the outer surfaces of the top and bottom waveguide walls adjacent the load pieces, and in part by air blown through the fins and across the load pieces through vent holes 74 in the narrow side waveguide walls, as by a fan (not shown). The vent holes 74 are dimensioned to minimize RF leakage while permitting air flow over the load.

The two parts 21 and 22 are held together at side flanges 81 and 82, respectively, at the load end of the second section 24, and at end flanges 83 and 84, respectively, at the remote side of the first section 23. They can be fastened by bolts 85 passing through holes 86 in these flanges or by other means, such as spring clips (not shown). Screws (not shown) can also be driven through the top and bottom walls 16, 15, respectively, of the main rectangular waveguide, into the flanges 37, 38 of the isolator, if desired, to assure good electrical contact between the waveguide and the isolator.

The circulator junction includes impedance matching members 91, 92, respectively, on the inside broad wall of each of the parts 21, 22, which are effective to reduce the transverse dimension (thickness) of the junction, generally as is described in US. Pat. No. 3,104,361 to Leetmaa, et al. The reactance of these matching members and the capacitance of the filter 26 (or both filters, if two are used) are so chosen and proportioned that the assembled component 20, when installed in the waveguide 10, will function as the combination of an impedance-matched isolator and a secondharmonic filter. If the filter 26 is omitted from both ends 27, 28 of the junction section 23, as is illustrated in FIG. 4, then additional impedance matching provisions (well-known, but not illustrated), will normally be made in the junction section 23. The form of the filters 26 that is used is not critical. While dumb-bell shaped slots have been illustrated, other forms such as a simple slot with straight or curved edges can be used. Other forms of impedance matching may be used in place of the illustrated triangular-shaped members 91, 92. For example, matching techniques described in the Wheeler US. Pat. No. 3,070,760, particularly in column 4 with respect to FIGS. 11 and 12, may be substituted.

The invention can be realized in an E-plane configuration, illustrated schematically in FIGS. 5 and 6. A main rectangular waveguide is provided with a rectangular aperture 102 in one of its wide walls 103. The aperture extends in length the full width of the waveguide, and the smaller dimension (width) of the aperture extends in one direction of the waveguides longitudinal axis. The isolator is comprised of a junction section 123 and a side-arm section 124, and. flanges 125 extend from the boundary between these sections, for mounting the isolator to the waveguide wide wall 103 when the junction section 123 is installed in the main waveguide. Ferrite members 126 are shown in the locations suitable for them in the junction section, but all other details of the isolator which are described above with reference to FIGS. 1-.3 have been omitted, to avoid unnecessary repetition. It will be understood, however, that features described in connection with the H-plane embodiment may be provided in the E-plane embodiment of the invention.

FIGS. 7, 8 and 9 show in a schematic way how an isolator realized in a three-port circulator may be modifled to feed back to a load energy that is reflected from the load back toward a source. The illustrated embodiment is a microwave oven 110, shown with its door 111 open and located in the oven is a load 112, such as a foodstuff to be cooked. The main waveguide 10 is coupled at one main arm 11 to a source of microwave energy 113, such as a Magnetron, and at the other main arm 12 to the interior of the oven via a main feed port 1 14 in the top wall 115. The branch waveguide section 24 of the circulator is coupled into the oven via a second port 109 in the top wall, so that energy reflected from the oven into the main waveguide feed arm 12, and thence via the circulator section 23 into the branch waveguide section 24, will be returned to the oven for use, rather than being absorbed in a dummy load. An attenuator 116 is fitted in the branch waveguide section 24 in place of the load pieces 71, 72, to partially absorb the reflected energy and thereby prevent resonance in the feed-back loop. A loss of about l-to-3 db is satisfactory for this purpose. The equivalent electrical circuit shown in FIG. 9 illustrates the feedback loop comprised of the branch waveguide section 24, attenuator 116 and a line section 109.

FIG. 10 shows how one part 21 of the isolator described above in connection with FIGS. l-3 can be modified in its branch waveguide section 24. A port section 109' is provided bounded by walls 20', and a flange 251 is provided at the foot of the end wall 25 for connecting, as by bolts 127 through holes 121 to the top wall 115 of the oven. One of the absorber load pieces 71 is thereby removed from the isolator, but the other load piece 72 may remain and this one can be tailored to function as the partial absorber or attenuator 1 16.

FIG. 11 is similar to FIG. 7, except that an E-plane isolator 120 is employed tofeed back to the oven 110,

via the branch waveguide 124, energy that is reflected from the oven through the waveguide feed section 130 of the main waveguide 100. A magnetron 131 is represented schematically at the input end of the main waveguide. It will be apparent that this arrangement employing an isolator realized with an E-plane junction lends itself to a more compact and less costly structure than does an arrangement using an l-l-plane junction. Energy propagating from the source 131 is fed into the oven 110 via the main waveguide 100 and feed 130, and energy that is'reflected back toward the source through the feed 130 is diverted into the oven via the branch waveguide 124, wherein suitable attenuation (not shown) can be provided.

FIG. 12 shows a modification of FIG. to permit the E-plane isolator to be dropped into the main waveguide 100 from the top. The mounting flanges 125 of FIG. 5 are shifted to the end wall of the junction section 123, where a plate 125' provides this function, and the waveguide 100 has two openings (not shown) in register in the opposite wide walls, corresponding to the opening 102 in FlG. 5.

We claim:

1. A three-port microwave waveguide junction circulator for use with a rectangular transmission line composed of wide walls having a known internal transverse width dimension and narrow wallshaving a known internal transverse height dimension, said waveguide having a rectangular aperture in one wall extending in a first dimension in and substantially coextensive with the internal transverse dimension of said one wall and in a second dimension a prescribed distance axially of said waveguide, said circulator comprising a section of rectangular waveguide enclosing the circulator junction and having first and second ports at its ends and a third port in a side wall, the external transverse dimensions of said waveguide junction section being only slightly smaller than the respective transverse internal inner dimensions of said transmission line and the axial length of said waveguide junction section being only slightly smaller than said second dimension of said rectangular aperture whereby said waveguide junction section can be installed in said transmission line through said rectangular aperture with the respective longitudinal axes of said transmission line and said waveguide junction section substantially parallel to each other and said third port accessible through said rectangular aperture, and means to hold said circulator in place in said transmission line when said waveguide junction section is so installed therein.

2. A circulator according to claim 1 including harmonic wave filter members disposed in at least one of said first and second ports.

3. A circulator according to claim 1 in which said waveguide junction section is made in two substantially identical parts each including portions of at least two rectangularly-related walls, the portions of at least one such wall terminating in respective edges that confront corresponding edges of the other part when said parts are assembled to form said waveguide junction section, and means to fasten said parts together when they are so assembled.

4. A circulator according to claim 1 in which said aperture is located in a narrow wall of said transmission line, and extends in width substantially coextensive with the internal height dimension of said transmission line, the long dimension of said aperture extending axially of said transmission line waveguide, and said section of rectangular waveguide forms an l-I-plane junction the first and second ports of which are disposed transverse to its longitudinal waveguide axis.

5. A circulator according to claim 1 in which said aperture is located in a wide wall of said transmission line, and extends in length substantially coextensive with the internal width dimension of said transmission line, the wide dimension of said aperture extending axially of said transmission line waveguide, and said section of rectangular waveguide forms an E-plane junction the first and second ports of which are disposed transverse to its longitudinal waveguide axis.

6. A circulator according to claim 1 including a thirdport waveguide coupled at one end to said third port and disposed substantially entirely outside said transmission line when said waveguide junction section is so installed therein.

7. A circulator according to claim 6 including a resistive load terminating said third port waveguide to form a two-port isolator.

8. In combination,- an isolator according to claim installed in said waveguide transmission line.

9. A circulator according to claim 6 in which said waveguide junction section and said third port waveguide are made in two substantially similar mating parts, each part including a wide wall of said junction section and a wide wall of said third port waveguide joined together, and portions of the narrow walls' of both upstanding therefrom, the narrow wall portions of each part being bounded by edges that confront the corresponding edges of the other part when said parts are assembled to form said circulator, and means to fasten said parts together when they are so assembled.

10. A circulator according to claim 9 in which each of said parts is a unitary casting.

11. A circulator according to claim 1 in which said waveguide junction section is made in two parts each including a wide wall and portions of a narrow wall the portions of said narrow wall terminating in respective edges that confront each other when said parts are assembled to form said waveguide junction section, said third port being located in the opposite narrow wall when said parts are so assembled, and means to fasten said parts together when they are so assembled.

12. A circulator according to claim 11 having wall members formed in the first and second ports of each part for partly closing said first and second ports, each of said wall members of each part having an edge which at its end regions is substantially in register with said edges of the narrow wall portions of said part, and which is recessed in its intermediate region to form with the corresponding wall member of the other part an iris opening to provide a harmonic wave filter when said parts are assembled.

13. A circulator according to claim 11 between said wide walls at least one ferrite circulator member, and resilient dielectric means dimensioned to be compressed when said parts are assembled, for holding said circulator member in place.

14. A circulator according to claim 13 in which there are two ferrite circulator members located one in contact with each of said wide walls and said dielectric means is located between said circulator members.

15. An isolator for detachable installation in a waveguide transmission line comprising a three-port microwave waveguide junction circulator having a substantially matched impedance termination at one port, said circulator comprising a section of rigid rectangular waveguide defining at its axial ends the two ports constituting first and second isolator ports and having said one port in a side wall, said waveguide section having external dimensions only slightly larger than its internal dimensions for enabling removal installation of said section entirely within another waveguide through an aperture in a wall of such other waveguide, and flange means on said waveguide section extending from the region of the periphery of said one port for engaging the exterior of said wall of such other waveguide, to install said isolator in such other waveguide transmission line with said isolator ports disposed transversely to the longitudinal axis insuch other waveguide to couple the microwave energy flowing therein, and said one port substantially in said aperture.

16. An isolator according to claim 15 having harmonic wave filter means in at least one of said isolator ports.

17. An isolator for detachable installation in a rectangular waveguide transmission line through an aperture in a side wall thereof comprising a three-port microwave waveguide junction circulator in a section of rectangular waveguide enclosing the circulator junction and having first and second ports at its ends oriented substantially transversely to its longitudinal axis and a third port in a side wall oriented parallel to said axis, the external transverse dimensions of said waveguide junction section being only slightly smaller than the corresponding internal transverse dimensions of said transmission line, a rectangular aperture in said side wall, the axial length of said waveguide junction section being only slightly smaller than the dimension of said rectangular aperture parallel to the transmission line longitudinal axis whereby said waveguide junction section can be installed in said transmission line through said rectangular aperture with the respective longitudinal axis of said transmission line and said waveguide junction section substantially parallel to each other and said-third port accessible through said rectangular aperture, said circulator including substantially matched impedance means for terminating said third-port and means to hold said isolator in placein said transmission line when said waveguide junction section is so installed therein, with said third-port terminating means external to said transmission line.

18. A circulator for detachable installation in a waveguide transmission line joining a source of microwave energy to a cavity which in use can be expected to re flect some of said energy back toward the source through said line, said circulator consisting of a threeport microwave waveguide junction circulator having only two ports constituting first and second transmission line ports and a third port for diverting such reflected energy out of said line, means to install said circulator in a waveguide transmission line with said transmission line ports disposed to couple to microwave energy flowing therein, and waveguide transmission line means to couple said third port directly to said cavity for returning at least some of said reflected energy to said cavity.

19. In combination, a three-port circulator type isolator in a waveguide transmission line joining a source of microwave energy to a cavity which in use can be expected to reflect some of said energy back toward the source through said line, said isolator having means to divert such reflected energy out of said line, and feedback transmission line means to return at least some of such diverted energy directly to the cavity for use therein.

20. A combination according to claim 19 including attenuator means in said feedback means to inhibit resonance in the feedback path of said reflected energy.

said feedback means.

@2 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,806,837 D t April 23, 1974 Inventor(s) .L Carr: 8 Sumner It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1 ,7 line 44, change "turned" to --tuned-- Column 5, line 37, change "storing" to shorting-- Column 6, line 25, delete "one" and insert the- Column 7, line 19, after "100" delete -and line 34, after "rectangular" insert -waveguide Signed and sealed this 15th day 9f July 1975.

(SEAL) Attest:

h C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Arresting Officer and Trademarks @3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORECTIN Patent No. 3,806,837 Dated April 23, 1974 Inventofls) .L Carr; S Sumner It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

ri I 1 Column 1, line 44, change "turned" to -tuned-- Column 5, line 37, change "storing" to --shorting- Column 6, line 25, delete "one" and insert -the-- Column 7, line 19, after "100" delete andline 34, after "rectangular" insert --waveguide- Signed and sealed this 15th day of July 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Arresting Officer and Trademarks 

1. A three-port microwave waveguide junction circulator for use with a rectangular transmission line composed of wide walls having a known internal transverse width dimension and narrow walls having a known internal transverse height dimension, said waveguide having a rectangular aperture in one wall extending in a first dimension in and substantially coextensive with the internal transverse dimension of said one wall and in a second dimension a prescribed distance axially of said waveguide, said circulator comprising a section of rectangular waveguide enclosing the circulator junction and having first and second ports at its ends and a third port in a side wall, the external transverse dimensions of said waveguide junction section being only slightly smaller than the respective transverse internal inner dimensions of said transmission line and the axial length of said waveguide junction section being only slightly smaller than said second dimension of said rectangular aperture whereby said waveguide junction section can be installed in said transmission line through said rectangular aperture with the respective longitudinal axes of said transmission line and said waveguide junction section substantially parallel to each other and said third port accessible through said rectangular aperture, and means to hold said circulator in place in said transmission line when said waveguide junction section is so installed therein.
 2. A circulator according to claim 1 including harmonic wave filter members disposed in at least one of said first and second ports.
 3. A circulator according to claim 1 in which said waveguide junction section is made in two substantially identical parts each including portions of at least two rectangularly-related walls, the portions of at least one such wall terminating in respective edges that confront corresponding edges of the other part when said parts are assembled to form said waveguide junction section, and means to fasten said parts together when they are so assembled.
 4. A circulator according to claim 1 in which said aperture is located in a narrow wall of said transmission line, and extends in width substantially coextensive with the internal height dimension of said transmission line, the long dimension of said aperture extending axially of said transmission line waveguide, and said section of rectangular waveguide forms an H-plane junction the first and second ports of which are disposed transverse to its longitudinal waveguide axis.
 5. A circulator according to claim 1 in which said aperture is located in a wide wall of said transmission line, and extends in length substantially coextensive with the internal width dimension of said transmission line, the wide dimension of said aperture extending axially of said transmission line waveguide, and said section of rectangular waveguide forms an E-plane junction the first and second ports of which are disposed transverse to its longitudinal waveguide axis.
 6. A circulator according to claim 1 including a third-port waveguide coupled at one end to said third port and disposed substantially entirely outside said transmission line when said waveguide junction section is so installed therein.
 7. A circulator according to claim 6 including a resistive load terminating said third port waveguide to form a two-port isolator.
 8. In combination, an isolator according to claim 7 installed in said waveguide transmission line.
 9. A circulator according to claim 6 in which said waveguide junction section and said third port waveguide are made in two substantially similar mating parts, each part including a wide wall of said junction section and a wide wall of said third port waveguide joined together, and portions of the narrow walls of both upstanding therefrom, the narrow wall portions of each part being bounded by edges that confront the corresponding edges of the other part when said pArts are assembled to form said circulator, and means to fasten said parts together when they are so assembled.
 10. A circulator according to claim 9 in which each of said parts is a unitary casting.
 11. A circulator according to claim 1 in which said waveguide junction section is made in two parts each including a wide wall and portions of a narrow wall the portions of said narrow wall terminating in respective edges that confront each other when said parts are assembled to form said waveguide junction section, said third port being located in the opposite narrow wall when said parts are so assembled, and means to fasten said parts together when they are so assembled.
 12. A circulator according to claim 11 having wall members formed in the first and second ports of each part for partly closing said first and second ports, each of said wall members of each part having an edge which at its end regions is substantially in register with said edges of the narrow wall portions of said part, and which is recessed in its intermediate region to form with the corresponding wall member of the other part an iris opening to provide a harmonic wave filter when said parts are assembled.
 13. A circulator according to claim 11 between said wide walls at least one ferrite circulator member, and resilient dielectric means dimensioned to be compressed when said parts are assembled, for holding said circulator member in place.
 14. A circulator according to claim 13 in which there are two ferrite circulator members located one in contact with each of said wide walls and said dielectric means is located between said circulator members.
 15. An isolator for detachable installation in a waveguide transmission line comprising a three-port microwave waveguide junction circulator having a substantially matched impedance termination at one port, said circulator comprising a section of rigid rectangular waveguide defining at its axial ends the two ports constituting first and second isolator ports and having said one port in a side wall, said waveguide section having external dimensions only slightly larger than its internal dimensions for enabling removal installation of said section entirely within another waveguide through an aperture in a wall of such other waveguide, and flange means on said waveguide section extending from the region of the periphery of said one port for engaging the exterior of said wall of such other waveguide, to install said isolator in such other waveguide transmission line with said isolator ports disposed transversely to the longitudinal axis in such other waveguide to couple the microwave energy flowing therein, and said one port substantially in said aperture.
 16. An isolator according to claim 15 having harmonic wave filter means in at least one of said isolator ports.
 17. An isolator for detachable installation in a rectangular waveguide transmission line through an aperture in a side wall thereof comprising a three-port microwave waveguide junction circulator in a section of rectangular waveguide enclosing the circulator junction and having first and second ports at its ends oriented substantially transversely to its longitudinal axis and a third port in a side wall oriented parallel to said axis, the external transverse dimensions of said waveguide junction section being only slightly smaller than the corresponding internal transverse dimensions of said transmission line, a rectangular aperture in said side wall, the axial length of said waveguide junction section being only slightly smaller than the dimension of said rectangular aperture parallel to the transmission line longitudinal axis whereby said waveguide junction section can be installed in said transmission line through said rectangular aperture with the respective longitudinal axis of said transmission line and said waveguide junction section substantially parallel to each other and said third port accessible through said rectangular aperture, said circulator including suBstantially matched impedance means for terminating said third-port and means to hold said isolator in place in said transmission line when said waveguide junction section is so installed therein, with said third-port terminating means external to said transmission line.
 18. A circulator for detachable installation in a waveguide transmission line joining a source of microwave energy to a cavity which in use can be expected to reflect some of said energy back toward the source through said line, said circulator consisting of a three-port microwave waveguide junction circulator having only two ports constituting first and second transmission line ports and a third port for diverting such reflected energy out of said line, means to install said circulator in a waveguide transmission line with said transmission line ports disposed to couple to microwave energy flowing therein, and waveguide transmission line means to couple said third port directly to said cavity for returning at least some of said reflected energy to said cavity.
 19. In combination, a three-port circulator type isolator in a waveguide transmission line joining a source of microwave energy to a cavity which in use can be expected to reflect some of said energy back toward the source through said line, said isolator having means to divert such reflected energy out of said line, and feedback transmission line means to return at least some of such diverted energy directly to the cavity for use therein.
 20. A combination according to claim 19 including attenuator means in said feedback means to inhibit resonance in the feedback path of said reflected energy.
 21. A combination according to claim 19 in which the cavity comprises a microwave heating enclosure.
 22. A combination according to claim 21 in which said enclosure has a first input at one end of said line for receiving energy from said source and a second input for coupling to said feed-back means for receiving therefrom energy reflected from the enclosure via said first input and diverted by the isolator from said line, and means coupling said second input directly to said feedback means. 